This invention relates to compositions which are useful as multiple polymeric additive systems. This invention also relates to processes for making multiple polymeric additive systems. This invention further relates to polymeric compositions that include a polymeric component and a multiple polymeric additive system. This invention even further relates to processes for preparing polymeric compositions that include a polymeric component and a multiple polymeric additive system.
Numerous molded articles and films are manufactured from one or more of a variety of polymeric resins. Often times, these resins, by themselves, do not possess all of the properties required by the end use for which they are made. To overcome their shortcomings, these resins are generally blended with other components which exhibit the desired properties. Such components are typically known in the industry as “polymeric additives”. There are many varieties of polymeric additives known, and each of these are available in a variety of physical forms (e.g., gas, liquid, solid, and combinations thereof) and chemical forms (e.g., organic, inorganic, metallic, non-metallic, polymeric, non-metallic, and combinations thereof).
Although polymeric additives can be made by a number of different ways, many are made by emulsion polymerization. Thereafter, the emulsion is dried to form a powder. The powder is then blended with the polymeric resin system whose properties need to be enhanced.
Accordingly, since many polymeric additives are blended with the polymeric resin when the additive is in a powder form, one significant limitation upon the development and/or selection of new polymeric additives is their ability to form a stable powder. The term “stable” as it pertains to powders means, among other things, the ability of the particles making up the powder to remain in a flowable form during normal storage, handling and processing procedures. One reason for the existence of this problem is that many polymeric additives are relatively soft. Accordingly, they often have the tendency to stick together; thus, reducing the additive's stability. This phenomenon is often seen in polymeric additives designed to enhance the impact modification of the polymeric resin system since, in order to impart this property, the additive generally needs to be soft and/or rubbery.
One means of addressing this problem has been to use multi-layered multiple polymeric additive systems. Such systems are typically known in the industry as a “core/shell” system. In most core/shell systems, the inner stage (i.e., the core) is relatively soft and/or rubbery; and the outer-stage (i.e., the shell) is relatively hard. The hardness of the outer shell keeps the particles from sticking together.
Polymer additives have also been developed for the purpose of modifying the processing characteristics of plastics resins. These “processing aids” are generally high in molecular weight, typically above 1 million g/mol, and are compatible with the plastic resin. However, dried processing aid powders are typically dusty and thereby difficult to handle.
It is therefore desirable to combine compositionally different polymeric additive particles to provide two or more functions, such as a combination of impact modifiers and processing aids. One way of combining an impact modifier polymeric additive particle with a processing aid polymeric additive particle is disclosed in U.S. Pat. No. 5,276,092. This Patent discloses core/shell impact modifier having an emulsion solids fraction less than 40% and processing aid additives which are prepared separately at small particle sizes by emulsion polymerization, co-agglomerated, further encapsulated by a final shell, and preferably isolated to a dry powder by spray-drying or coagulation.
While the use of co-agglomeration and an encapsulating shell polymer has been used to provide emulsion blends of two compositionally different polymeric additive particles, such aqueous systems are still fraught with other problems. For example, these aqueous systems are limited to low (less than 40%) solids weight fractions having more than 60% by weight water. Ordinarily, this water needs to be removed so that the process of preparing blends of resins and such aqueous dispersions is inefficient in requiring the removal of such large quantities of water.
Often times, the isolation of polymeric additive particles as dried powders will vary depending on the physically and chemical composition of the particle. Accordingly, co-isolating two or more different additive particles is at best complicated. For example, the problems seen during the co-isolation of impact modifiers and processing aids typically result in dispersion problems of the additives into the resins because one of the additive particles may have a greater affinity for the liquid phase, or be a lot more or a lot less stable as a colloid in the liquid phase, and therefore the distribution of polymeric additive particles in such a co-isolated powder will vary. For example, it is typical that during co-isolation, one population of particles will isolate separately from the other population. Accordingly, avoiding the need to co-isolate multiple polymeric additive particles is desirable in avoiding these problems.
Notwithstanding the aforementioned problems associated with powdery plastic additive systems, they are still the additive system of choice. However, the industry continues to look for alternatives to such systems. One of the alternatives that has been suggested is disclosed in U.S. Pat. No. 3,864,432. The multiple polymeric additive system disclosed in this Patent is not in a powder form, yet it is used to improve the impact strength of PVC resins. U.S. Pat. No. 5,276,092 also discloses that the emulsion product of encapsulated, co-agglomerated core/shell impact modifier and processing aid additives are preferably isolated to a dry powder by spray-drying or coagulation, but may be used still in an emulsion form.
While such a system can be used, there are many advantages associated with using higher solids systems that provide either improved property enhancements and/or two or more property enhancements. For example, some of the advantages of using higher solids systems that provide improved property enhancements include combining polymeric additives wherein at least one of the additives is not readily isolatable as a powder. Specifically, in the area of impact modification, it is desirable to add rubbery materials to brittle plastics in order to increase their ability to absorb impact stress. Although typical impact modifiers are in the form of core/shell polymer particle powders, it is desirable to further incorporate other rubbery materials which often are not readily available in a powder form. One example of a rubbery material which is not readily isolatable as a powder, includes solution-polymerized rubbery polymers such as solution-made styrene/diene block copolymers. Other rubbery materials which are desirable for incorporation into multiple polymeric additive systems include rubbery emulsion polymer particles which are not readily isolatable in a powdery form. Yet other rubbery materials which are desirably incorporated into impact modifying polymeric additive compositions include liquid polymers which are not readily isolatable as a powder. Examples of such liquid polymer include a polymeric oil, such as: low molecular weight polybutene, polysiloxane, certain mineral oils, liquid polysulfide, and the like.
For example, some of the advantages of using higher solids systems that two or more property enhancements include combining polymeric additives wherein at least one of the polymeric additives is an impact modifier and the other polymeric additive is a processing aid.
Many plastics additives which are not necessarily polymeric are also commonly used in the plastics industry to modify the processability and/or properties of polymeric resins. Examples of these other additives include: waxes; pigments; opacifiers; fillers; exfoliated clays; toners; antistatic agents; metals; flame retardants; thermal stabilizers; antioxidants; cellulosic materials; internal lubricants; external lubricants; oils; rheology modifiers; powder flow aids; dispersing aids; UV stabilizers; plasticizers; fillers; optical modifiers; surface roughness modifiers; surface chemistry modifiers; adhesion modifiers; surface hardeners; compatibilizers; diffusion barrier modifiers; stiffeners; flexibilizers; mold release agents; processing modifiers; blowing agents; thermal insulators; thermal conductors; electronic insulators; electronic conductors; biodegradation agents; antistatic agents; internal release agents; coupling agents; flame retardants; smoke-suppressers; colorants, and the like, and/or combinations thereof.
As seen by the examples set out above, many plastics additives come in a variety of physical forms such as volatile liquids, pasty waxes, dusty powders, hard solids, and the like. Accordingly, they are often handled separately when formulating a polymeric composition containing these additives. This creates obvious problems, especially when some of the additives come in a liquid form, while others that are needed come in a powder form. Other inherent problems with the conventional ways of enhancing the properties of a polymeric composition through the use of a polymeric additives include: handling dusty powders which requires special handling to avoid breathing of powders, explosion hazards arising from static electricity build-up, contamination, general difficulty in handling and containing dusty materials; handling pellets requires separate operational processes than that of powders making processes more complex and/or expensive requiring further equipment; minor ingredients (such as low solid fraction) are difficult to handle and evenly disperse in polymeric resins using conventional processes.
Notwithstanding the problems associated with conventional multiple polymeric additive systems, they will almost always be necessary due to the inherent deficiencies of polymeric compositions. However, the industry is continually searching for improved multiple polymeric additive systems which resolve at least some of the aforementioned problems.